Token tree
A token tree is a recursive Rust macro syntax structure consisting of tokens and nested delimited sequences of tokens.
Write Powerful Rust Macros
A Rust token tree is a syntactic token or delimited sequence of tokens that can be captured as a broadly permissive macro fragment.
- How it is used
- Captures and forwards broadly shaped macro input when narrower declarative fragments cannot express it.
- How deep it goes
- Defines TokenTrees within TokenStreams and demonstrates matcher capture and direct procedural-macro inspection, while deferring complete syntax parsing.
- Examples
- Uses a `lazy_static!` trailing matcher and a derive macro that extracts a struct or enum name.
- What you can do after
- Apply it via `macro_rules!` matchers or procedural TokenStream iteration when macro input must be captured or inspected.
Idiomatic Rust
A token tree is a recursive syntactic structure containing tokens, sequences of tokens, or nested token trees for macro matching.
- How it is used
- Supports variadic macro matching and forwards arbitrary argument token sequences to another macro.
- How deep it goes
- Defines recursive token trees, repetition quantifiers, and transcription, but does not develop broader macro parsing internals.
- Examples
- Uses special_println!, println!, format!, format_args!, and var_print! to demonstrate capture, forwarding, and repeated identifiers.
- What you can do after
- Build macro_rules! matchers that capture repeated token trees and replay them in an expansion.
Learn Rust in a Month of Lunches
A token tree is a syntactic token or delimited group of tokens that can be matched and repeated by a Rust macro.
- How it is used
- Explains how declarative macros accept and repeat flexible input.
- How deep it goes
- Defines `tt` and demonstrates repetition, but stops short of compiler internals behind built-in macros.
- Examples
- Uses `write!`, `format_args!`, and `todo!` to show single, repeated, empty, and formatted token-tree inputs.
- What you can do after
- Evaluate macro definitions to infer whether they accept one, many, optional, or formatted inputs.
Read how Learn Rust in a Month of Lunches explains token tree →
Related concepts
- TokenStreampart of · TokenStream is a sequence of Rust source tokens used as input or output during procedural macro expansion and code generation.
- recursive data structurekind of · A recursive data structure is a structure whose definition directly or indirectly refers to another instance of the same structure.
- fragment specifieruses · A fragment specifier is a declarative-macro matcher annotation that specifies the syntactic category of tokens a metavariable can match.
- token-tree fragment specifierused by · A token-tree fragment specifier is a Rust declarative-macro matcher specifier that matches a token tree, including delimited groups.
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